Is a voltage overrated fuse ok?
Is a voltage overrated fuse ok?
(OP)
I have a client who has 27kV fuses on an 11kV system (on overhead lines). I am not a fuse expert and would like to know if this is a good idea. The 27kV fuse will be longer in length than an 11kV one, and I am wondering how this affects fuse performance?
Thanks.
Thanks.






RE: Is a voltage overrated fuse ok?
Regards
Marmite
RE: Is a voltage overrated fuse ok?
RE: Is a voltage overrated fuse ok?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Is a voltage overrated fuse ok?
Fuses designed to interrupt the arc quickly produce a higher voltage than those which interrupt the arc slower.
This arc voltage must be limited to the system withstand voltage.
The arc voltage produced by the 27kV fuse would be greater than that of an 11kV fuse and may exceed the 11kV system withstand voltage.
RE: Is a voltage overrated fuse ok?
Please note that the fuse characteristics will only provide the current and time curves, without mentioning the voltages. So how it can give rise to higher voltage?
RE: Is a voltage overrated fuse ok?
"Peak arc voltage is dependant upon the number of constrictions in an element, because of the arcs in series. This gives a minimum value of peak arc voltage irrespective of the applied voltage up to a certain point. When this point is exceeded, the extra applied voltage can force the arcing to persist and produce burn-back and other effects which may increase with each incremental voltage, thus causing a larger peak arc voltage. It is therefore clear that a fuse of higher voltage rating should not be used to replace a blown fuse of lower voltage rating unless due cognisance is taken of the fact that its peak arc voltage will be greater. Peak arc voltage must not exceed the dielectric withstand of the system in which the fuse is placed."
The above is based on the fact that HV fuse designs (is not just simply a single solitary wire) but consist of a fuseable element with constrictions along its length. It is at the constrictions that melting first occurs, resulting in a series of small arcs along the length of the fuse. The arcing voltage can be around 600V/inch and is independent of the applied voltage as stated above. Note that this is a very generalised description as alloys are sometimes introduced to delay the melting time (using the M-effect) thus resulting in a fuse with a delayed characteristic.
RE: Is a voltage overrated fuse ok?
Regards
Marmite
RE: Is a voltage overrated fuse ok?
RE: Is a voltage overrated fuse ok?